Different visual representations of audio data are commonly used to display different features of the audio data. For example, a frequency spectrogram shows a representation of frequencies of the audio data in the time-domain (e.g., a graphical display with time on the x-axis and frequency on the y-axis). Audio data can be edited. For example, the audio data can include noise or other unwanted components (e.g., one or more incorrect pitches).
A pitch is the perceived fundamental frequency of a sound. While the actual fundamental frequency can be precisely determined through physical measurement, it may differ from the perceived pitch because of overtones, or partials, in the sound. Perceived pitch can depend on the amplitude of the sound, especially at low frequencies. For instance, a low bass note will sound lower in pitch if it is louder. Frequency is the measurement of the number of occurrences of a repeated event per unit of time. To calculate the frequency of the event, the number of occurrences of the event within a fixed time interval are counted, and then divided by the length of the time interval. For example, the frequency of the standard pitch A above middle C is usually defined as 440 Hz (440 cycles per second). An occurrence of the standard pitch A above middle C at 450 Hz (450 cycles per second), would then likely sound out of tune (e.g., sharp) to the listener. Similarly, an occurrence of the standard pitch A above middle C at 430 Hz (430 cycles per second), would also likely sound out of tune (e.g., flat) to the listener.
Removing or editing unwanted audio components improves audio quality (i.e., the removal of noise components provides a clearer audio signal, and the removal of incorrect pitches provides a more accurate and pleasing audio signal). Alternatively, a user may apply different processing operations (e.g., edits), to portions of the audio data to generate particular audio effects.
Audio editing by frequency, for example, typically involves pitch shifting an entire selected frequency range by the same ratio. Pitch shifting is a sound recording technique, in which the normal pitch or tone of a sound is altered (e.g., shifted), for effect or for other purposes (e.g., to tune an out-of-tune pitch). Pitch shifting may be done both in analog and in digital recording and usually involves no more than a half-step (semitone) or possibly whole step (whole tone) change to the pitch. In digital recording, pitch shifting is accomplished through digital signal processing.
To apply a pitch shifting effect on a particular frequency, for example, an entire frequency range is selected. The entire frequency range is then copied into a new (e.g., blank), file and pitch shifted. Current pitch shifting algorithms are not designed to be implemented on specific frequency ranges (e.g., a range of 100 Hz to 200 Hz), and thus the entire selected frequency range is edited (e.g., shifted) by the same ratio.